This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A180752 #7 Jul 22 2025 08:28:13 %S A180752 0,1,1,2,3,7,14,31,67,148,325,717,1580,3485,7685,16950,37383,82451, %T A180752 181850,401083,884615,1951080,4303241,9491097,20933272,46169785, %U A180752 101830665,224594602,495358987,1092548639,2409691878,5314742743 %N A180752 Half the number of nX3 binary arrays with each element equal to at least two neighbors. %C A180752 Column 3 of A180760 %H A180752 R. H. Hardin, <a href="/A180752/b180752.txt">Table of n, a(n) for n=1..99</a> %F A180752 Empirical: a(n) = 2*a(n-1) + a(n-2) - a(n-3) - a(n-5). %F A180752 Empirical: G.f.: -x^2*(-1+x+x^3+x^2) / ( (x-1)*(1+x)*(x^3+2*x-1) ). a(n)-a(n-2) = A052980(n-3). - _R. J. Mathar_, Mar 24 2018 %K A180752 nonn %O A180752 1,4 %A A180752 _R. H. Hardin_ Sep 20 2010